Gene Mapping Worksheet
1. In 1911, Thomas Hunt Morgan collected the following crossover gene frequencies
while studying Drosophila. Bar-shaped eyes are indicated by the B allele, and
carnation eyes are indicated by the allele C. Fused veins on wings (A) and scalloped
wings (S) are located on the same chromosomes.
Gene Combinations
A/B
A/C
B/C
B/S
A/S
C/S
Recombination Frequency
2.5%
3.0%
5.5%
5.5%
8.0%
11.0%
2. The following chart shows the crossover frequencies for some genes on an autosome
of organism Z. Construct a chromosome map.
Genes
P&Q
P&R
P&S
Q&R
Q&S
Crossover Frequency
5%
8%
12%
13%
17%
3. For a series of experiments, a linkage group composed of genes W, X, Y and Z was
found to show the following gene combinations. (All recombinations are expressed
per 100 fertilized eggs). Construct a gene map.
Genes
W
X
Y
Z
W
–
5
7
8
X
5
–
2
3
Y
7
2
–
1
Z
8
3
1
–
4. For a series of breeding experiments, a linkage group composed of genes A, B, C, and
D was found to show the following gene combinations. (All recombinations are
expressed per 100 fertilized eggs). Construct a chromosome map.
Genes
A
B
C
D
A
–
12
15
4
B
12
–
3
8
C
15
3
–
11
D
4
8
11
–
5. In Drosophila, the gene for eye color (A), wing shape (B), and body color (C) are all
found on the same chromosome. The following crossover frequencies for these genes
were determined by experiments.
Genes
A&B
A&C
B&C
Crossover Frequency
12.5%
6.0%
18.5%
What is the correct sequence of the genes A, B and C on the chromosome?
6. Construct a gene map given the following information:
Genes
A&B
A&C
C&D
A&F
F&B
D&F
Crossover Frequency
24.0%
8.0%
2.0%
16.0%
8.0%
6.0%
Challenge Question:
7. Five traits found in Drosophila are yellow body color (y), white eye color (w),
vermilion eye color (v), miniature wing (m) and rudimentary wing (r). Given the
following crossover frequencies, construct a genetic map.
Genes
y&w
v&m
v&r
v&w
v&y
w&m
y&m
w&r
Crossover Frequency
2.2%
3.0%
26.6%
30.0%
32.2%
33.0%
35.2%
56.6%
8. There are 3 genes on a single chromosome: A, B, and C. They exhibit the following
crossing over frequencies:
a. A-B = 35%
b. B-C = 10%
c. C-D = 15%
d. C-A = 25%
e. D-B = 25 %
Determine the order of the genes on the chromosome.
9. Genes A, B, and C are linked genes. A testcross shows that the recombination
frequencies between A and B is 28%, and between A and C is 12%. Can you
determine the linear order of these genes? Explain.
10. Determine the sequence of genes along a chromosome based on the following
recombination frequencies:
f. A-B = 8%
g. A-C = 28%
h. A-D = 25%
i. B-C = 20%
j. B-D= 33%
11. 4. Determine the sequence of genes along a chromosome based on the following
recombination frequencies:
k. A-B = 30%
l. A-C = 9%
m. A-D = 18%
n. B-C = 21%
o. B-D = 12%
p. E-D = 12%
q. E-A = 6%
r. E-C = 3%
s. E-B = 24%
12. Use the table below to map the genes found on this chromosome of a fruit fly.
13. A space probe discovers a planet inhabited by creatures who reproduce with the same
hereditary patterns seen in humans. Three phenotypic characters are height (T = tall, t
= short), head appendages (A = antennae, a = no antennae), and nose morphology (S
= upturned snout, s = downturned snout). Earth scientists are able to do some
controlled breeding experiments on them using various heterozygotes. For a tall
heterozygote with antennae cross, the offspring are: tall/antennae - 46,
dwarf/antennae - 7, dwarf/no antennae - 42, tall/no antennae - 5. For a heterozygote
cross with antennae and an upturned snout the offspring were: antennae/upturned 47, antennae/downturned snout - 2, no antennae/downturned snout - 48, no
antennae/upturned snout -3. Calculate the recombination frequencies for both traits.